Tendou was just walking back from extra practice at school on a Saturday (they had to practice every day) when he noticed some kid sitting on the curb. He didn't recognize them, so probably some kid from a different school.

The kid was just sitting there, and Tendou was too curious not to go up to them. So Tendou walked over and nudged them with his foot. Not the politest way to get someone's attention but who cares.